(WJW) – There are now answers as to what caused the deaths of thousands of birds.

The birds were found dead in northern Utah waterways between September and early October due to a suspected outbreak of avian botulism, according to state officials.

The Utah Division of Wildlife Resources (DWR) said in a media release that biologists first discovered dead and sick birds in mid-September.

“Avian botulism occurs almost yearly in Utah — typically between July and September — particularly during periods when the weather is really hot and after periods of rainfall. Those conditions often create stagnant pools of water that hold and grow the anaerobic bacteria that causes avian botulism,” the DWR wrote. “However, this year, a particularly large number of birds were impacted.”

Avian botulism is a paralytic, often fatal, disease of birds that results from the ingestion of a toxin produced by a bacteria, Clostridium botulinum. The toxin is produced when there are low oxygen levels and warm water temperatures.

Footage released by the agency shows hundreds of dead birds floating on the water.

“Many birds have been collected and submitted for disease testing. The birds tested negative for highly pathogenic avian influenza,” the DWT said. “While final test results are still pending, biologists suspect the birds died of avian botulism.”

The agency said the disease is “not typically associated with human illness,” but warned waterfowl hunters to avoid interacting with sick or weak birds, to cook any meat thoroughly, and to keep diseased meat away from dogs, which can be affected by botulism.